Can anyone help please??

Hi we own a 2009 Zafira B 1.7CDTI diesel . Car has been great however last weds while my partner was driving it lost power and cut out and he was unable to accelerate. He got towed home. The car turns over but won’t start instead it coughs and splutters it’s definitely trying to but there’s just nothing. The car has had aWe had a friend look at the car as he thought it sounded like a injector issue however the friend unscrewed the top of the 4th injector and is now unable to screw it back on which I guess is going to make it harder getting that injector out? Also there seems to be a black casing surrounding the 4 injectors which’s makes getting the injectors out impossible in the 1st pictures I’ve uploaded. We are tight on money due to COVID 19 and taking to a garage or even having a mechanic looking at it let alone having the work done would take months and months to save for my partner relays on the car For his job And no car = no work. He’s managed to borrow a car for a week so we are really hoping it’s an easy fix . Can anyone firstly tell us if the casing surrounding the 4 injectors needs to totally come off? How easy is it going to be to get the injector with no top on out? Any help would be great . Thank you